1. Field of Invention
The present invention relates to a mechanical device for exploiting oil, and more particularly to a tower frame pumping unit.
2. Description of Related Arts
In the field of exploiting oil, the beam pumping unit is gradually replaced by the tower frame pumping unit because the tower frame pumping unit has a simple structure, low costs, small energy consumption and etc. However, some mutually related technical problems existing in the tower frame pumping unit affects and limits wider promotion and application thereof. The two most predominant technical problems are the method for giving space to drill and the duration of steel wires. Before drilling, in order to save enough space for the drilling devices to operate at the well mouth, a minimum distance between the tower frame and the well mouth should be kept more than 700 mm. Thus two most common methods for giving space to drill are as follows. The first one is to set the whole tower frame movable. Before drilling, the whole tower frame is dragged away from the well mouth by traction devices. Because main devices of the tower frame pumping unit are provided on the top of the tower frame to form a relatively high center of gravity, it is time-consuming, energy-consuming and relatively insecure to integrally move the tower frame. The second one is to provide a guiding wheel extending outwardly at the top of the tower frame. A distance at which the guiding wheel extends outwardly can be adjusted based on practical needs, so the distance between the tower frame and the well mouth is possibly kept longer than 700 mm during installing the tower frame. Considering stability and costs of the tower frame, usually a diameter of the guiding wheel is relatively small; moreover, the duration of the steel wires is closely related with a bending diameter thereof, and the steel wires continuously passes a rope wheel and the guiding wheel in a short distance, so that the steel wires continuously bend twice under a condition that stresses thereof are not completely removed, which accelerates damaging the steel wires. FIG. 1 shows a diagram of duration factors relative to bending fatigue of the steel wires. Supposing that a ratio of a bending diameter D of the steel wires to a diameter d of the steel wires is 62 and the duration factor of the steel wires is 1, the bigger ratio, the longer duration. Conventionally, a tower frame pumping unit with a load within 12 tons has a ratio of the diameter of the guiding wheel to the diameter of the steel wires only around 40 to 50; a tower frame pumping unit with a load over 12 tons has a ratio of the diameter of the guiding wheel to the diameter of the steel wires only around 25 to 35. Thus a relatively small diameter of the guiding wheel leads to a relatively short duration of the steel wires. Some conventional tower frame pumping units use belts to replace the steel wires to solve the problem of the duration of the steel wires, but the belts would shake violently under actions of winds, which tends to damage a suction rod of the pumping unit and the well mouth. The conventional tower frame pumping units fail to simultaneously overcome the above technical problems.